The dimensional precision of half shell parts, which are fabricated by drawing a blank, is regularly subject to quality problems in production. High demands in dimensional precision are set particularly in automotive engineering, since the half shell parts must frequently mate with other components or half shell parts or be joined to these. The dimensional precision of converted blanks is substantially affected by the fact that stresses are induced in the blanks by shaping processes, which becomes apparent after conversion due to springback of the converted blank. This substantially reduces the dimensional precision of the converted blank and renders the production process for high precision components considerably more difficult. Up to now this problem has been solved by a preform being produced in order to convert this in a further tool to the end form. By the intermediate step of producing a preform, on the one hand, the strains induced by the shaping step are not so great. On the other hand, however, relatively high costs arise due to the intermediate step of producing an intermediate form. Above all, the material-shaping tools for the preform, but also the increase in production times, as a result of two separate working steps, lead to a cost burden on the total process until the finished component is produced.
German Patent Application DE 197 42 818 A1 discloses the production of a structural member for motor vehicles, having a reinforcing plate, which by deepenings and projections creates a shaping reserve for forming the base plate and the reinforcing plate. The reinforcing plate provided with projections and deepenings is intended to prevent the formation of wrinkles or tears during common shaping with the base plate. The German Patent Application mentioned is concerned with the shaping of reinforced or “patched” blanks. Although, for the reinforcing plate, tears and formation of wrinkles can be prevented during conversion by creating shaping reserves in the form of bulges, the dimensional precision of the converted blank outside the reinforced region is not improved.
European Patent EP 1 708 832 B1 discloses hydro-forming of a blank with bulges and/or deepenings, wherein the maximum natural strain is to be increased by the bulges/deepenings. Hydro-forming is only applicable in combination with closed hollow profiles. Therefore, no half shells are produced with this process. In addition, the working-media based forming is very time-consuming and relatively expensive compared to conventional deep-drawing.